Chandra X-Ray Observations of Nineteen Millisecond Pulsars in the Globular Cluster 47 Tucanae

Abstract

We present spectral and long-timescale variability analyses of \textit{Chandra} ACIS-S observations of the 19 millisecond pulsars (MSPs) with precisely known positions in the globular cluster 47 Tucanae. The X-ray emission of the majority of these MSPs is well described by a thermal (blackbody or neutron star hydrogen atmosphere) spectrum with a temperature $T_{\mathrm{eff}}\sim (1-3)\times 10^6$ K, emission radius $R_{\mathrm{eff}}\sim 0.1-3$ km, and luminosity $L_X\sim 10^{30-31}$ ergs s${}^{-1}$. For several MSPs, there is indication that a second thermal component is required, similar to what is seen in some nearby field MSPs. The radio-eclipsing binary MSPs 47 Tuc J, O, and W show a significant non-thermal component, with photon index $\Gamma \sim 1-1.5$, which may originate in an shock formed due to interaction between the relativistic pulsar wind and matter from the stellar companion. We re-examine the X-ray--spindown luminosity relation ($L_X-\dot{E}$) and find that due to the large uncertainties in both parameters the result is consistent with both the linear $L_X-\dot{E}$ relation and the flatter $L_X\propto {\dot{E}}^{0.5}$ predicted by polar cap heating models. In terms of X-ray properties, we find no clear systematic differences between MSPs in globular clusters and in the field of the Galaxy.

13 pages, 6 figures, accepted for publication in the Astrophysical Journal

References in corpus (1)

• GBT Discovery of Two Binary Millisecond Pulsars in the Globular Cluster M30

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